Transmission Cooler Lines

Replace transmission cooler lines that run between the automatic transmission and radiator-mounted transmission cooler, preventing leaks and maintaining proper transmission cooling.

Warnings

Tools required

Parts

• Transmission cooler line set (inlet and outlet) × 1 — Use OEM specification or quality aftermarket with correct fittings
• Transmission cooler line fittings/O-rings × 1 — Often included with line set
• Mopar ATF+4 × 2 — MS-9602

Fluids

• Mopar ATF+4 — 2 qt

Preparation

1. Park vehicle on level surface and apply parking brake
2. Place wheel chocks behind rear wheels
3. Allow transmission to cool if recently driven (minimum 30 minutes)
4. Raise front of vehicle with floor jack and support securely on jack stands at frame rails
5. Position drain pan under transmission cooler line connections at radiator
6. Locate transmission cooler lines running from transmission to radiator (lower driver side of radiator)
7. Identify inlet and outlet lines and trace routing to note clip and bracket locations

Procedure

1. 1

   Disconnect cooler lines at radiator
   Using a flare nut wrench, carefully loosen the cooler line fittings at the radiator-mounted transmission cooler. The fittings are typically 3/8" or 1/2" depending on year. Turn counterclockwise slowly to avoid stripping. Expect 1-2 quarts of ATF to drain from lines into drain pan. Once loose, unthread fittings by hand and allow lines to drain completely.
2. 2

   Disconnect cooler lines at transmission
   Move drain pan under transmission cooler line connections at transmission case (passenger side, near pan rail). Use flare nut wrench to loosen fittings at transmission. These connections may be tight due to heat cycling. Once loosened, unthread by hand and allow additional fluid to drain. Cap or plug transmission ports immediately with clean shop rags to prevent contamination.
   ⚠Do not allow dirt or debris to enter transmission ports. Even small particles can cause valve body damage.
3. 3

   Remove line mounting clips and brackets
   Trace the cooler lines from transmission to radiator and locate all mounting clips and brackets. On 4WD models, trace the lines and note the actual routing along the frame rail (typically 4-6 clips); verify routing side against the vehicle as it may differ from generic guidance. Remove clips by prying spring tabs or removing retaining bolts as applicable. Note exact routing and clip positions for reinstallation. Some clips may be attached to transfer case skid plate or crossmember.
4. 4

   Remove old cooler lines
   Carefully maneuver old cooler lines out from between frame rails, avoiding sharp edges that may snag. On trucks with transfer case, lines route around transfer case - work carefully to avoid damaging other components. Inspect removed lines for failure location (cracks, corrosion, rubbing damage) to ensure replacement lines won't encounter same issue.
5. 5

   Inspect and clean fittings
   Inspect transmission and radiator cooler ports for debris, metal shavings, or damaged threads. Use wire brush to clean radiator fitting ports. Remove rags from transmission ports one at a time and inspect for metal particles (indicator of internal damage). Clean transmission port threads with wire brush. If old lines used compression fittings with O-rings, ensure O-ring grooves are clean and undamaged.
   ℹ️Presence of excessive metal particles in transmission fluid may indicate internal transmission wear requiring further inspection.
6. 6

   Prepare new cooler lines
   Unpack new cooler lines and verify correct length and fitting types match original. If lines came with new O-rings or seals, install them onto fittings per manufacturer instructions. Lightly coat threads and O-rings with clean ATF+4 for easier installation and proper sealing. Identify which line is inlet (from transmission to cooler) and outlet (from cooler to transmission) - typically marked or different lengths.
7. 7

   Route new cooler lines
   Starting from transmission side, carefully route new lines along frame rail following exact path of original lines. On 4WD models, ensure lines clear transfer case with adequate clearance for movement. Verify lines do not contact sharp edges, exhaust components, or moving parts. Leave fittings loose at both ends until routing is confirmed correct.
   ⚠Ensure minimum 1 inch clearance from exhaust components to prevent heat damage to cooler lines.
8. 8

   Install mounting clips and brackets
   Install all mounting clips and brackets in original locations to secure cooler lines to frame rail. Clips should hold lines firmly but not crush them. On models with bolted brackets, tighten bolts snug but do not overtighten - typically hand-tight plus 1/4 turn. Verify lines cannot vibrate or move excessively when tugged by hand.
9. 9

   Connect cooler lines at transmission
   Thread transmission-side fittings into transmission case ports by hand until snug, ensuring they thread smoothly without cross-threading. Once hand-tight, use flare nut wrench to tighten an additional 1/2 to 3/4 turn until snug. Do not overtighten - verify the OEM cooler line fitting torque for this transmission (e.g., 47RE/48RE) in the service manual, and tighten by feel to avoid stripping the transmission case threads. Fitting should be firm but not excessively tight.
   ⚠Transmission case threads are aluminum and easily stripped. Tighten fittings carefully and stop if excessive resistance is felt.
10. 10

    Connect cooler lines at radiator
    Thread radiator-side fittings into transmission cooler ports by hand until snug. Use flare nut wrench to tighten an additional 1/2 to 3/4 turn. Same caution applies - do not overtighten. Ensure both lines are connected to correct ports (inlet and outlet) - consult service manual if uncertain, as reversed flow can cause transmission damage.
11. 11

    Add transmission fluid
    Remove transmission dipstick (locate the transmission fill tube/dipstick at the rear of the engine; verify exact side against the vehicle). Using funnel, add 2 quarts of Mopar ATF+4 to replace fluid lost during line replacement. This is initial fill only - additional fluid will be added after system is purged of air. Reinstall dipstick.
12. 12

    Purge air and check for leaks
    Start engine and allow to idle in Park. Have assistant observe all cooler line connections for leaks while you monitor from driver seat. If leaks appear, shut off engine immediately and tighten affected fitting. With engine idling, shift through all gear ranges (P-R-N-D-2-1) pausing 3 seconds in each, then return to Park. This circulates fluid through cooler system and purges air. Check connections again for leaks.
    ⚠️Keep hands and tools clear of rotating components while engine is running. Do not reach near cooling fan or belts.
13. 13

    Check and adjust fluid level
    With engine at idle in Park, check transmission fluid level on dipstick. Fluid should be in "cold" range. Add ATF+4 as needed in 1/2 quart increments, rechecking after each addition. Do not overfill. Shut off engine, lower vehicle from jack stands, and take 10-15 minute test drive to bring transmission to operating temperature.

Reassembly

1. After test drive, recheck transmission fluid level with engine running at operating temperature - fluid should be in "hot" range on dipstick
2. Top off fluid as needed to bring to proper level
3. Perform final inspection of all cooler line connections and mounting clips
4. Wipe down any spilled ATF from frame rails and components to prevent dirt accumulation

Verification

• Verify no ATF leaks at any cooler line connections after test drive
• Confirm transmission fluid level is in proper "hot" range on dipstick with engine running
• Verify all mounting clips are secure and cooler lines do not vibrate excessively at idle
• Check that transmission shifts smoothly through all gears without slipping or delayed engagement
• Verify adequate clearance between cooler lines and exhaust components, driveshaft, and suspension
• Monitor fluid level and check for leaks after 50-100 miles of driving

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